1. Field of the Invention
The present invention is directed to an antenna arrangement with shielding for a nuclear magnetic resonance tomograph apparatus, and in particular to an antenna arrangement of the type wherein the antenna is composed of planar conductor structures arranged at the circumference of an examination space and extending in the longitudinal direction thereof, antenna being partially covered with shielding elements that are connected to a shielding that surrounds the examination space.
2. Description of the Prior Art
An antenna arrangement of the above type is disclosed in European Application 0 105 550. The antenna disclosed therein is composed of two radio-frequency coils extending in the longitudinal direction of the examination space. The interspace between the conductors of the radio-frequency coils proceeding in the longitudinal direction of the examination space is bridged with a comb-like structure of conductive elements. The electrical field around the conductor is thus shielded, so that a fixed stray capacitance between the conductors and the comb-shaped structure is achieved in addition to a higher Q-factor for the radio-frequency coil. This stray capacitance is minimally influenced by the geometry or nature of an examination subject. The necessity of balancing the radio-frequency circuit dependent on the examination subject is thus eliminated.
In the comb structure of European Application 0 105 550, all individual elements are connected to one another at one side and are grounded outside the radio-frequency coil. This, however, has the disadvantage that there are relatively long conductor paths are necessary--particularly for the middle elements of the comb structure--having a not inconsiderable inductance to the grounding point.
The shielding effect is reduced due to the inductance.